Virtual Evaluation of Ceramic Glow Plug Design using Multiphysics Simulation Approach

A glow plug is generally used to assist the starting of diesel engines in cold weather condition. Low ambient temperature makes the starting of diesel engine difficult because the engine block acts as a heat sink by absorbing the heat of compression. Hence, the air-fuel mixture at the combustion chamber is not capable of self-ignition based on air compression only. Diesel engines do not need any starting aid in general but in such scenarios, glow plug ensures reliable starting in all weather conditions. Glow plug is actually a heating device with high electrical resistance, which heats up rapidly when electrified. The high surface temperature of glow plug generates a heat flux and helps in igniting the fuel even when the engine is insufficiently hot for normal operation. Durability concerns have been observed in ceramic glow plugs during testing phase because of crack formation. Root cause analysis is performed in this study to understand the reasons of the cracking of the glow plug when it is subjected to in-operation conditions and design optimization is suggested to reduce the risk of cracking. Multiphysics based simulation methodology is developed to capture the overall behavior of glow plug during manufacturing and in-operation conditions. Rapid heating of glow plug by passing of electricity is captured using a coupled electro-thermal simulation approach and the stress developed due to thermal gradients is also captured by a thermo-structural analysis. Effect of different operational parameters over the directional stresses are studied using the developed simulation approach to optimize the glow plug design. Stress comparison results between the existing model and the proposed optimized model is also presented in this paper to demonstrate the improvement in durability behavior of the optimized design compared to the initial design of glow plug. Simulation methodology described in this paper can be used as a decision making tool during initial design stages of glow plug to come up with robust designs.